This invention relates to an infrared-transparent bi- or multicomponent chalcogenide glass based on selenium and germanium, as well as to optical fibers and optical elements made of such glass.
A general discussion of chalcogenide glasses is found in "Glass: Science and Technology", Uhlmann and Kreidl, Vol. 1, Glass-Forming Systems, pages 231-299, Academic Press, New York, 1983, with particular reference to germanium selenium glasses being found on pages 251-254.
These glasses are transparent at a wavelength range of between about 0.9 .mu.m and about 17 .mu.m for this reason, they are beneficially utilized in the infrared range, for example, for optical fibers for the transmission of CO.sub.2 laser light and for infrared detectors.
The conventional chalcogenide glasses, however, exhibit, at a wavelength of 12.8 .mu.m, an absorption due to contamination with traces of oxygen and resultant Ge-O lattice vibrations. The trailing end of this absorption band extends to the wavelength 10.6 .mu.m, so that this glass shows relatively high absorption losses in transmitting infrared radiation in the CO.sub.2 laser region.
According to DOS No. 1,621,015, the residual oxygen of the melt, introduced by the manufacturing process and by the starting compounds, can be removed by addition of a reducing agent, such as, for example, carbon or aluminum.
DOS No. 3,443,414 discloses a chalcogenide glass for optical fibers in the infrared region wherein this absorption band is likewise suppressed with aluminum, gallium, or indium.
Hilton et al. (Journal of Non-Crystalline Solids, 17:319-338 [1975]) mention, besides aluminum, also zirconium and copper. Silver, magnesium, and potassium chloride are described therein as being of low efficacy.
The above-mentioned doping media exhibit, in part, considerable drawbacks in the production of chalcogenide glasses. Carbon displays a relatively poor reactivity with respect to residual oxygen. Moreover, carbon tends to form agglomerates which, being light scattering centers, are disadvantageous especially in laser-optic applications.
Doping with aluminum is permissible only in very small amounts since aluminum has a strongly corrosive effect on the silica glass crucibles. As a consequence of corrosion, Si-O lattice vibrations are observed in the chalcogenide glass, the absorption band of which lies at about 9.5 .mu.m and thus exerts a deleterious influence on transmission at a wavelength of 10.6 .mu.m employed for the CO.sub.2 laser. Furthermore, the corrosion weakens the strength of the crucible and thus reduces plant safety which is of particular importance when producing chalcogenide glasses. Moreover, due to the strongly corrossive action of aluminum, the useful life of the silica glass crucibles is diminished, thereby resulting in an increase in manufacturing costs.
The maximum aluminum addition of 100 ppm indicated in DOS No. 3,443,414, and the simultaneously required purity of the starting materials of 99.999%, are, in the final analysis, limits resulting from the corrosive property of aluminum.
Copper and zirconium dopants are effective only at relatively high concentration (1 to 2 atom %), whereby the physical and optical characteristics of the glass are materially altered.